The present invention provides a rear cover of a flat panel electronic device and a flat panel electronic device having the rear cover. A outer surface of the rear cover is provided with a recess and a supporting leg, the supporting leg is pivotably connected in the recess through a pivot means so as to enable the supporting leg to pivot between a retracting position and an unfolding position, the supporting leg is configured to be contained in the recess when being in the retracting position, and to make an angle with the rear cover when being in the unfolding position, a speaker is disposed in the supporting leg, sound holes are disposed at a position on a side wall of the supporting leg which is corresponding to the speaker, a through-hole is formed at a position of the rear cover which is corresponding to the pivot means, and an electric wire of the speaker passes through the through-hole to extend into the rear cover. The angle of the screen of the flat panel electronic device relative to the user can be adjusted through the supporting leg of the rear cover to improve the user's comfort level in watching, and the surface to be placed (such as the table surface) has no influence on the sound effect.